#include <linux/module.h>
#include <linux/types.h>
#include <linux/fs.h>
#include <linux/errno.h>
#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/cdev.h>
#include <asm/io.h>
//#include <asm/system.h>
#include <linux/uaccess.h> 
//#include <asm/uaccess.h>
#include <linux/slab.h>   /* kmalloc */

#define GLOBALMEM_SIZE 0x1000  /*全局内存大小:4KB*/
#define MEM_CLEAR 0x1          /*清零全局内存*/
#define GLOBALMEM_MAJOR 0      /*预设的 globalmem 的主设备号,如果设置为0，就使用动态申请主设备号*/

/*增加自动创建设备节点代码*/
static struct class *globalmem_cls;
static struct device *globalmem_device;

static unsigned int globalmem_major=GLOBALMEM_MAJOR;
/*globalmem 设备结构体*/
struct globalmem_dev
{
	struct cdev cdev;                     /*cdev 结构体*/
	unsigned char mem[GLOBALMEM_SIZE];  /*全局内存*/
};

struct globalmem_dev *globalmem_devp; /*设备结构体指针*/

/*文件打开函数*/
int globalmem_open(struct inode *inode, struct file *filp)
{
	/*将设备结构体指针赋值给文件私有数据指针*/
	filp->private_data = globalmem_devp;
	return 0;
}

/*文件释放函数*/
int globalmem_release(struct inode *inode, struct file *filp)
{
	return 0;
}


/* ioctl 设备控制函数 */
static long globalmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
	struct globalmem_dev *dev = file->private_data;/*获得设备结构体指针*/
	switch (cmd)
	{
		case MEM_CLEAR:
			memset(dev->mem, 0, GLOBALMEM_SIZE);
			printk(KERN_INFO "globalmem is set to zero\n");
			break;
		default:
			return - EINVAL;
	}
	return 0;
}

/*读函数*/
static ssize_t globalmem_read(struct file *filp, char __user *buf,size_t size,loff_t *ppos)
{
	unsigned long p = *ppos;
	unsigned int count = size;
	int ret = 0;
	struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/

	/*分析和获取有效的写长度*/
	if (p >= GLOBALMEM_SIZE)
		return count ? - ENXIO: 0;
	if (count > GLOBALMEM_SIZE - p)
		count = GLOBALMEM_SIZE - p;

	/*内核空间→用户空间*/
	if (copy_to_user(buf, (void*)(dev->mem + p), count))
	{
		ret = - EFAULT;
	}
	else
	{
		*ppos += count;	
		ret = count;
		printk(KERN_INFO "read %d bytes(s) from %ld\n", count, p);
	}
	return ret;
}


static ssize_t globalmem_write(struct file *filp, const char __user
		*buf,size_t size, loff_t *ppos)
{
	unsigned long p = *ppos;
	unsigned int count = size;
	int ret = 0;
	struct globalmem_dev *dev = filp->private_data; /*获得设备结构体指针*/

	/*分析和获取有效的写长度*/
	if (p >= GLOBALMEM_SIZE) //要写的偏移位置越界
		return count ? - ENXIO: 0;
	if (count > GLOBALMEM_SIZE - p) //要写的字节数太多
		count = GLOBALMEM_SIZE - p;

 	/*用户空间→内核空间*/
	if (copy_from_user(dev->mem + p, buf, count))
		ret = - EFAULT;
	else
	{
		*ppos += count;
		ret = count;
		printk(KERN_INFO "written %d bytes(s) from %ld\n", count, p);
	}
	return ret;
}


/* seek 文件定位函数 */
static loff_t globalmem_llseek(struct file *filp, loff_t offset,int orig)
{
	loff_t ret = 0;
	switch (orig)
	{
		case 0:
        /*相对文件开始位置偏移*/
        if (offset < 0)
        {
            ret = - EINVAL;
            break;
        }
        if ((unsigned int)offset > GLOBALMEM_SIZE)
        {
            ret = - EINVAL;
            break;
        }
        filp->f_pos = (unsigned int)offset;
        ret = filp->f_pos;
        break;
		case 1:		/*相对文件当前位置偏移*/
        if ((filp->f_pos + offset) > GLOBALMEM_SIZE)
        {
            ret = - EINVAL;
            break;
        }
        if ((filp->f_pos + offset) < 0)
        {
            ret = - EINVAL;
            break;
        }
        filp->f_pos += offset;
        ret = filp->f_pos;
        ret = - EINVAL;
        break;
		default:
        ret= - EINVAL;
        break;
	}
	return ret;
}

/*文件操作结构体*/
static const struct file_operations globalmem_fops =
{
	.owner = THIS_MODULE,
	.llseek = globalmem_llseek,
	.read = globalmem_read,
	.write = globalmem_write,
	.compat_ioctl = globalmem_ioctl, 	/* ioctl */
	.open = globalmem_open,
	.release = globalmem_release,
};

/*初始化并注册 cdev*/
static void globalmem_setup_cdev(struct globalmem_dev *dev, int index)
{
	int err, devno = MKDEV(globalmem_major, index);
    /*字符设备注册*/
	cdev_init(&dev->cdev, &globalmem_fops);
	dev->cdev.owner = THIS_MODULE;
	dev->cdev.ops = &globalmem_fops;
	err = cdev_add(&dev->cdev, devno, 1);
	if (err)
		printk(KERN_NOTICE "Error %d adding LED%d", err, index);

    /*创建设备文件节点*/
    globalmem_cls = class_create(THIS_MODULE, "class");
	if(IS_ERR(globalmem_cls))
	{
		unregister_chrdev(globalmem_major,"globalmem");
        printk(KERN_NOTICE "class create error\n");
		return -EBUSY;
	}

    /*生成 mknod /dev/globalmem */
	globalmem_device = device_create(globalmem_cls,NULL,devno,NULL,"globalmem");
	if(IS_ERR(globalmem_device))
	{
		class_destroy(globalmem_cls);
		unregister_chrdev(globalmem_major,"globalmem");
        printk(KERN_NOTICE "device_create error\n");
		return -EBUSY;
	}
}


/*设备驱动模块加载函数*/
int globalmem_init(void)
{
	int result;
    /*MKDEV是将主设备号和次设备号转换成dev_t类型*/
	dev_t devno=MKDEV(globalmem_major,0);

	/* 申请字符设备驱动区域*/
	if ( globalmem_major)
	{
		result=register_chrdev_region(devno,1,"globalmem");
	}
	else
	/* 动态获得主设备号 */
	{
		result=alloc_chrdev_region(&devno,0,1,"globalmem");
        /*获取主设备号*/
		globalmem_major=MAJOR(devno);
	}
	if (result < 0)
		return result;

	/* 动态申请设备结构体的内存*/
	globalmem_devp=kmalloc(sizeof(struct globalmem_dev),GFP_KERNEL);

	if(!globalmem_devp) /*申请失败*/
	{
		result= - ENOMEM;
		goto fail_malloc;
	}

	memset(globalmem_devp, 0, sizeof(struct globalmem_dev));
	/*设置字符驱动结构体*/
    globalmem_setup_cdev(globalmem_devp, 0);
    printk(KERN_NOTICE "globalmem_init\n");
	return 0;

fail_malloc:
    unregister_chrdev_region(devno, 1);
    printk(KERN_NOTICE "globalmem_init fail\n");
	return result;
}

/* 模块卸载函数 */
void globalmem_exit(void)
{
	cdev_del(&globalmem_devp->cdev);   /*删除 cdev 结构*/
	kfree(globalmem_devp); /*释放设备结构体内存*/
	unregister_chrdev_region(MKDEV(globalmem_major,0),1); /*释放设备号*/
    if(globalmem_cls != NULL)
        class_destroy(globalmem_cls);
    printk(KERN_NOTICE "globalmem_exit\n");
}

/* Module info */
MODULE_AUTHOR("Joe Jiang");
MODULE_LICENSE("Dual BSD/GPL");
module_param(globalmem_major,int,S_IRUGO);
module_init(globalmem_init);
module_exit(globalmem_exit);
